The invention relates to oxygen sensors for generating a low voltage signal in response to differences in oxygen partial pressures on opposite sides of a solid electrolyte cell such as zirconia stabilized with yttria. In automotive applications where temperatures in the exhaust stream are generally sufficiently high to meet the approximately 425.degree. C. minimum desirable requirements of a zirconia sensing cell, it has been conventional practice to locate the zirconia cell near the center of the exhaust stream where the temperature usually runs approximately 535.degree. C. Where the sensing cell has been made in the form of a disc mounted in a metal tube, problems of sealing the disc against gas leakage have been encountered due to differences in the temperature coefficient of expansion. Other workers in this field have proposed utilizing zirconia in closed end, elongated thimble form to permit sealing to be accomplished at the cool end of the thimble where differential expansion is inconsequential. Such elongated thimbles are, however, quite expensive and fragile.